1. Field of the Invention
The present invention relates to a class-D amplifier for audio application.
2. Description of the Related Art
An audio instrument uses a class-D amplifier widely for resulting in a rise in efficiency, downsizing it and saving the weight thereof. Japanese Patent Application Publication No. 2002-204149 discloses that the class-D amplifier includes a half-bridge switching amplifying unit composed of a pair of switching elements or a full-bridge switching amplifying unit composed of two pairs of switching elements and a driver unit for driving the switching amplifying unit. The driver unit receives a pulse width modulation (PWM) signal that is obtained by pulse-width-modulating an analog signal or a PWM signal containing a signal that is obtained by performing single-bit A/D conversion on an analog signal. The driver unit controls one of the switching elements paired in the switching amplifying unit so that it can be switched on or off at same phase as that of the received PWM signal. The driver unit also controls the other switching element so that it can be switched on or off at a phase opposite to that of the received PWM signal. A switching signal that is pulse-amplified by such the switching on or off of the switching elements is band-limited using a low pass filter, thereby realizing an amplified analog signal.
When driving the paired switching elements based on driving signals from the driver unit, if the switching elements of hi-side and low-side are switched on at the same time, a large shoot-through current may occur, thereby causing excessive heat to generate and/or such the element to be broken down therefor. Thus, in a class-D amplifier, a dead-time setting unit is provided to delay a timing for switching a switching element on so that the large shoot-through current may be prevented from being flown therethrough by setting the dead time that the switching elements of hi-side and low-side are switched off at the same time. If, however, the dead time is too long, a reproduced audio output from a speaker may be distorted seriously, thereby degrading audio quality. Therefore, a period of time for the dead time is so designed that a trade-off of an occurrence of the shoot-through current and an audio quality can be achieved.